James Reece is an agent with the CIA.
Well, almost. He will eventually start to work for/with them though he would not likely ever think of himself, let alone announce himself, as such. He will be proven to them, not willingly by him, to be an asset that is just too tempting to not use.
Reece kills people. From a distance, sometimes a very long distance. As a sniper, he is considered one of the best and there are a considerable number of people who are no longer walking above ground that could testify to that, had they still been breathing. That is the talent that the Agency will find so appealing and, unfortunately for Reece, so much in demand.
When we first meet him, in the initial recorded adventure, he is on a very serious mission but not for the Agency nor the government for which he served in the military for some time, rising to the rank of Lieutenant Commander in the Navy SEALS. This mission is one of his choosing and one that he takes even more seriously than all those the Service called on him to do, actions that "happen when an apex predator, a warrior at the top of his game, is thrown into a situation from which there is no return'. This mission is one of personal vengeance and it will take a large toll on him and his friends.
Oh, one other small thing causing trouble for Reece is a brain tumor. That would be enough to get to most people but considering the other troubles Reece has to deal with, well, it just needs to stand in line.
After his mission of justice is completed, he is approached by the Agency with a job offer and while he really had no great love of the idea, he knew he needed to do something. Finding meaningful work which made use of his finely honed skillset was not likely otherwise, unless he went the mercenary route, so he accepts, reluctantly.
Of course, considering the life that Reece had before we meet him and especially considering what he had after we meet, the relationship with the Agency is going to be a very bumpy one.